1. Field of the Invention
The present invention relates to lithography devices and more particularly, to revolving filters to control light transmittance and transmittance profile.
2. Description of the Related Art
Lithography devices have been used in the fabrication processes of semiconductor devices, liquid crystal displays, magnetic thin film heads, imaging devices and micro devices etc., and in doing so, lithography devices have been used to form mask or reticule patterns on wafers coated with a sensitizer (e.g., photoresist) or a glass plate etc. In lithography devices, light intensity and intensity profile should be maintained conformal. If not, depending on light intensity or intensity profile, patterns, which are formed through masks or reticules on a substrate, may be unsharp. As a result, there is difficulty in obtaining a wanted CD (Critical Dimension). Specifically, with high-integration circuits, decreased line width is sensitively influenced by light intensity and intensity profile.
Now, when parallel rays are vertically incident on a boundary surface of a plane, transmittance can be written asTransmittance=(It/Io)×100, where incidence intensity is Io and transmittance intensity is It.
In Japanese Laid-Open Publication No. 09-266159, light intensity is controlled by a revolver, revolvers, or a revolver and a plurality of plane filters arranged parallel to the revolver and a plurality of transmittance control filters.
In Korean Laid-Open Publication No. 2003-0024638, light intensity profile is controlled using condenser lens distortion or by interposing at least two filters.
However, the light profile irradiating a subject changes according to various light profile shapes (e.g., conventional, annular, quadrupole and dipole). The intensity uniformity of light also varies with changing NA or SIGMA conditions. Furthermore, the intensity uniformity of light varies based on whether a device is used or not. In this case, intensity uniformity can be represented by
      Intensity    ⁢                  ⁢    uniformity    =                    intensity        ⁢                                  ⁢        located        ⁢                                  ⁢        in        ⁢                                  ⁢        a        ⁢                                  ⁢        certain        ⁢                                  ⁢        position                    average        ⁢                                  ⁢        of        ⁢                                  ⁢        entire        ⁢                                  ⁢        intensity              ×    100  
FIG. 1 shows intensity uniformity in a slit depending on illuminating conditions.
The abscissa axis (or x-axis) represents intensity measurement number for equally spaced measurements taken while moving from one side of a shot to another through a slit. In other words, if the slit length is about 26 mm in the long axis, the measurements are taken by moving 2.6 mm between each measurement, thus resulting in 11 measurements. The ordinate axis (or y-axis) represents intensity uniformity. Intensity uniformity can be represented by
      Intensity    ⁢                  ⁢    uniformity    =                    intensity        ⁢                                  ⁢        in        ⁢                                  ⁢        each        ⁢                                  ⁢        position                    entire        ⁢                                  ⁢        intensity        ⁢                                  ⁢        of        ⁢                                  ⁢        light        ⁢                                  ⁢        profile              ×    100  
In FIG. 1, intensity uniformity is measured when a transmittance profile filter is used and illuminating conditions are changed. Referring to FIG. 1, since light intensity at both ends is greater than the average intensity, intensity uniformity values are 100% and higher.
In this case, A, C and Q represent annular, conventional and quadrupole, respectively. While, 1, 1′ and 3, 3′ represent different illuminating conditions, that is, different values of NA and SIGMA.
As shown in FIG. 1 the irradiated subject light intensity profile varies according to the changing illuminating mode (e.g., annular, conventional and quadrupole), as well as the changing NA and Sigma conditions.
FIG. 2 shows variation of light intensity according to the duration of continuous device use. The abscissa axis represents week number. For example, WK10 represents 10 weeks of continuous device use. The ordinate axis represents the ratio (referred to as “intensity profile trend” hereinafter) of the sum and difference of both the maximum and minimum values of intensity profile (mathematical equation 1). Intensity profile can be obtained in the same way as was described for FIG. 1 and can be written as
                              Max          ⁢                                          ⁢                      Int            .                                                  ⁢                          -                                                          ⁢              Min                                ⁢                                          ⁢                      Int            .                                    Max          ⁢                                          ⁢                      Int            .                                                  ⁢                          +                                                          ⁢              Min                                ⁢                                          ⁢                      Int            .                                              [                  Mathematical          ⁢                                          ⁢          equation          ⁢                                          ⁢          1                ]            where, Max Int. represents the maximum value of intensity uniformity and Min Int. represents the minimum of intensity uniformity.
As shown in FIG. 2, intensity uniformity dramatically changes after about 36 weeks.
Accordingly, it is required that light intensity as well as light intensity profile are controllable in a fabrication device.